The present invention relates to a method of forming dough pieces of uniform weight. In particular, this invention relates to a method of continuously sensing the mass loading of a strip of dough and adjusting dough thickness according to the mass loading values before cutting into pieces to maintain uniform dough piece weight.
"Mass loading" for purposes of this disclosure is a weight per unit area of a sheet of dough.
Commercially manufactured dough products are commonly rolled into a sheet and machined with a series of rollers of decreasing gap distance to achieve a desired dough thickness before cutting. The dough is then cut into pieces and packaged for consumer purchase and use.
When manufacturing dough products, it is desirable to maintain a selected target weight product. Overfilling can be costly and can cause the containers to rupture or not seal properly, and underfilling can lead to consumer complaints. It is desirable from a consumer acceptance standpoint as well as a cost standpoint to maintain carefully controlled product weight.
Some refrigerated biscuit and roll doughs are grouped and sold as a group in a spiral wound composite container, such as with refrigerated biscuit dough, for example. When packaging a number of pieces of dough in a single container, it is even more important to maintain a constant weight in each dough piece such that when the pieces are combined, the combined weight of the pieces and container is within an acceptable range of product weight. In general, the larger the number of pieces of dough per container, the more important it is to control the mass loading of the sheet before cutting the pieces.
When dough has rheological properties which cause the dough to spring-back during processing, it is often difficult to control dough piece weight. For example, when the thickness of a sheet of dough is reduced by being passed through rollers having a selected gap distance between opposing rollers, and the resulting dough thickness exceeds the selected gap distance, the dough is said to have "spring back." Dough which has spring back is frequently undergoing pressure flow when passing through the final pair of calendar rollers, which ultimately determines finished cut dough piece thickness. Pressure flow exists when the central portion of the sheet as viewed in cross-section flows at a faster speed than at the outer edges.
The prior art recognizes that the design of a process control system for machining dough should compensate for the flow regime of the dough as described in Spinelli et al. U.S. Pat. No. 4,849,234, column 2, line 38 through column 3, line 31. The process control method shown in Spinelli controls the mass flow rate of a sheet of dough by controlling roller speeds in a series of rollers. The method calculates roller speed ratios to maintain a selected mass flow rate and then trims the individual roller speeds in response to sensed variations in dough consistency. Col. 4, line 66 through Col. 5, line 2.
Hayaski U.S. Pat. No. 5,124,163 shows a method of delivering a sheet of dough of a constant volume by measuring the sheet thickness between an upper pair of opposing rollers and a lower pair of opposing rollers. The speed of the upper pair of rollers is controlled, while the speed of the lower pair of rollers remains constant. The signal from a thickness sensor located on either side of the dough sheet between the upper pair of rollers and the lower pair of rollers is input into a controller which controls the speed of the upper pair of rollers. The distance between opposing lower rollers, or "gap distance" remains constant during operation of the rollers. This method controls dough sheet volume, not dough weight per unit area.
A device is shown in Ban et al. U.S. Pat. No. 5,106,636 which continuously measures the thickness, width and weight of a sheet of dough. The specific weight of the dough is continuously calculated. This data is used to adjust the thickness of a dough strip with a stretching system to make cut dough pieces.
The device shown in Ban et al. includes a hopper and a pair of vertical conveyors positioned below the hopper. The pair of rollers positioned beneath the vertical conveyors reduce the thickness of the sheet of dough. After passing through the first set of rollers, the thickness and weight are measured in the sheet. If the weight per unit time does not equal a predetermined value, the speed of the conveyor is adjusted such that roughly a constant mass of dough is delivered per unit time.
FIG. 1 shows a portion of the process control scheme disclosed in Ban et al. The control loop described above for delivering a roughly constant mass of dough from the first set of rollers is not shown in this Figure. The portion of the process which illustrates how the final dough thickness is determined is shown, however.
The sheet passes through a first stretching device which includes first, middle and second conveyors located beneath the sheet, and an elliptical roller mechanism located above the sheet. After the sheet passes through the first stretching device, the weight, thickness and width of the dough are measured and the specific weight of the dough is calculated, as shown in FIG. 1. A target specific weight is also input into the controller, and the calculated specific weight is compared to the target specific weight. A signal representing the difference between the target specific weight and actual specific weight is generated.
The operator uses the dimensional information to evaluate the rheological properties of the dough. For example, the operator can determine whether or not the dough is too elastic by comparing the width of the sheet to reference values, for example. Then, the composition of the next batch of dough can be adjusted.
A second stretching device is provided. The signal generated by comparing the target and actual specific weights is fed forward and is used to calculate the height of the lower surface of the elliptical roller relative to the upper surface of the lower conveyor, near the exit end of the elliptical roller. The height is then adjusted, which adjusts the dough sheet thickness.
When the dough is strongly plastic, the process further adjusts the sheet thickness by increasing the speed of the third conveyor after the roller mechanism is lifted based on the following formula: EQU V.sub.2 =(T.times.V.sub.1)/T
where V.sub.1 is the velocity of the second conveyor, T is the dough strip thickness and V.sub.2 is the adjusted third conveyor velocity.